1. Field of the Invention
The instant invention relates to a method and an apparatus for fragmenting a substance by discharging pulsed electrical energy through the substance. More specifically, the pulsed electrical energy is discharged through the substance via a plurality of electrodes located in the substance.
2. Brief Description of the Prior Art
The prior art has long recognized the potential of electrical energy to break or fragment a solid substance. This potential has been particularly recognized in the field of underground mining and in the formation and production of subterranean wells. In these areas, it is often necessary to fracture a hard, solid substance, such as rock, to advance the face of the mining shaft, or to increase the production from an underground well by fracturing the surrounding subterranean area.
The earliest attempts at utilizing electrical energy to fragment rocks involved placing a plurality of resistance electrodes in holes formed in the rock and subsequently passing an electric current through the electrodes. The heating of the rock by the electrodes eventually caused it to fracture along the path of the electrodes due to thermal stresses induced in the rock. Apparatus for inducing thermal stresses in rock to advance a mine face are also known. These devices typically utilize electrode arcing to heat the rock face and cooling means to cool the face after the application of the electric arc. This cyclical heating and cooling induces thermal stresses within the rock face which subsequently cause it to fragment. The more modern devices utilize this basic technology of heating or heating/cooling steps, but use electron beams or high velocity plasma jets to accomplish the heating.
It is also known to apply electrical impulses to substances such as rocks to cause them to fracture. The electrical impulses establish an electrical current path between electrodes applied to the rock through naturally occuring lower resistance paths. The current then causes the vaporization and expansion of liquids contained within the rock, which expansion exerts internal pressure causing the rock to fracture. Alternatively, the rock may be treated with a liquid, such as an electrolyte solution, prior to the application of electrical pulses to assist in the establishment of an electrical path between the electrodes. Where the rock is not pre-treated with a liquid solution, it may be necessary to utilize multipoint electrodes in order to establish a current path between the electrodes through the rock.
Electrical pulses have also been utilized as part of a two-stage process for rock fragmentation. Electrical pulses cause numerous micro-fractures in the rock, which is subsequently caused to fragment along these fractures by the application of accoustical energy.
Electrical energy may also be used to drill into a hard substance, such as rock. The prior art is replete with various forms of spark drills which depend upon an arc between either a pair of electrodes, or an electrode and the surrounding formation itself to cause it to fracture. The electrodes may be utilized by themselves or in combination with a standard roller cone drill bit.
None of the prior art apparatus has proven to be efficient from an energy consumption standpoint. The input energy required by these devices in order to accomplish their purposes within a reasonable amount of time has proven to be economically unsound, especially in view of the constantly rising energy costs. Any device which relies upon the heating of the rock or the liquid contained in a rock, must, of necessity, have a high energy input or require energy input over a relatively long period of time.